The role of specific dietary factors in cancer prevention has been assessed through epidemiologic studies and animal experiments. For many of these agents, information is incomplete concerning their quality and form in the food supply, bioavailability, biochemical effects and interaction with other nutrients. To further define these parameters in the human population, a cooperative research effort between the Beltsville Human Nutrition Research Center (BHNRC) and the Cancer Prevention Studies Branch, DCPC, is being conducted. Investigations of the trace element selenium (Se) has been done during the first year. The initial phase of the Se studies examines the pharmacokinetics of a single oral dose of selenite and selenometionine in a healthly population. The second phase will examine the bioavailability and health effects of multiple doses of inorganic and organic selenium. A study will then be done correlating dietary intake of beta-carotene with beta-carotene levels, retinol and retinol-binding protein levels in the blood. Improved methods for analyzing carotenoids and retinoids in food and blood samples have been developed. A study will be done correlating dietary intake of beta-carotene levels, retinol and retinol-binding protein levels in the blood. The effect of changing dietary fat levels and saturation of ovarian and adrenal hormones will be studied in a free-living population. This study will be explanatory to two trials of a low fat diet being conducted by the Diet and Cancer Branch. This study will also evaluate the role of dietary fat in fecal mutagen production.